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Bryx_Electronics > Electricity and Magnetism > Flashcards

Electricity and Magnetism Flashcards

1
Q

Electrical current is defined as what?

A

charge per unit time

I=Q/t, Q=coulombs t=seconds

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2
Q

Atom with net charge of either positive or negative

A

Ion

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3
Q

Negative ion

A

Anion

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4
Q

Positive Ion

A

Cation

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5
Q

The force required to move charges in a material

A

Voltage

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6
Q

Different names for voltage

A

Electromotive force(emf), Potential Difference

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7
Q

Volts formulas

A

V=W/C

W=work, Joules
C=Charge, Coulombs
*1 volt = 1 Joule/Coulomb

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8
Q

opposition or hindrance offered by the material to current flowing

A

Resistance

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9
Q

Ohm is named after whom?

A

Georg Simon Ohm

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10
Q

Resistance Formula

A

R=pL/A

p=resistivity
L=length
A=cross sectional area

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11
Q

What is the equivalent if 1 mil?

A

1/1000 inch

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12
Q

A Square mil is equal to?

A

pi/4 circular mil

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13
Q

Temperature effect on resistance formula

A

R2/R1=(|T|+t2)/(|T|+t1)
R2=R1(1+α(t2-t1))
α=1/(|T|+t1)

α=temperature coefficient of resistance at t1
T=inferred absolute zero temp
-234.5 for annealed copper

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14
Q

the property of material to aid or allow the flow of charge

A

Conductance

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15
Q

Conductance Formula

A

G=1/R

G=A/pL

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16
Q

Amount of work done in a circuit per unit time

A

Electrical Power

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17
Q

Power formulas

A 
P=W/t
P=QV/t
P=IV
P=V^2/R
P=I^2R
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18
Q

What are the common resistivity(ρ) of:

Aluminum,

A

ρ = 2.6 x10^-8 ohm-m

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19
Q

What are the common resistivity(ρ) of:

Brass,

A

ρ = 6 x10^-8 ohm-m

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20
Q

What are the common resistivity(ρ) of:

Carbon,

A

ρ = 350 x10^-8 ohm-m

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21
Q

What are the common resistivity(ρ) of:

Nichrome,

A

ρ = 100 x10^-8 ohm-m

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22
Q

What are the common resistivity(ρ) of:

Silver

A

ρ = 1.5 x10^-8 ohm-m

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23
Q

What are the common resistivity(ρ) of:

Tungsten

A

ρ = 5.6 x10^-8 ohm-m

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24
Q

Temperature resistance coefficient (α, Not thermal expansion) of:
Annealed copper

A

α20 = 0.00393

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25
Q

Temperature resistance coefficient(α, Not thermal expansion) of
Nickel

A

α20=0.006

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26
Q

Temperature resistance coefficient of(α, Not thermal expansion)
Iron

A

α20=0.0055

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27
Q

engineering prefix

nano

A

1x10^-9

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28
Q

engineering prefix

pico

A

1x10^-12

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29
Q

engineering prefix

femto

A

1x10^-15

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30
Q

engineering prefix

atto

A

1x10^-18

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31
Q

A substance that possesses magnetism property and can attract iron and other ferromagnetic materials including ferrites (non metallic ferromagnetic materials)

A

Magnet

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32
Q

The place where magnet was discovered

A

Magnesia

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33
Q

the magnet is called _____ by ancient people

A

Lodestar (early guiding stars)

Iron oxide called magnetite (Fe3O4)

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34
Q

It is produced by electric current rather than a natural magnet

A

Electromagnetism

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35
Q

Who discovered the phenomenon of electromagnetism?

A

Hans Christian Oersted (april 21, 1820)

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36
Q

A property possessed by magnetic materials by the virtue of which residual magnetism is possible

A

Retentivity

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37
Q

The magnetism left after the removal of the magnetizing force

A

Residual Magnetism

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38
Q

The opposite of retentivity

A

Coercivity

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39
Q

It is required to counter retentivity to eliminate residual magnetism

A

Coercive force

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40
Q

How can a magnet lose its properties?

A

Tax evasion. jk, When it is heated, hammered, or dropped from a height

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41
Q

Tractive/Lifting force of a magnet formula

A

F=.5(AB^2)/u0
A=total area of contact, m^2
B=flux density, Wb/m^2 or T`

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42
Q

What is the first law of magnetism

A

Like poles repel and unlike poles attract

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43
Q

What is the second law of magnetism

A

A magnetic field always tends to arrange itself that the greatest number of lines of force are created

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44
Q

What is the domain theory of magnetism

A

The magnetic property of a material is due to the electron’s spin direction. In non-magnetic materials, the net magnetic field is zero since electron’s spin cancels each other, while in magnetic materials the magnetic fields are aligned thus forming small bar magnet

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45
Q

What is the molecular/Weber theory of Magnetism?

A

The molecules of a material are magnets themselves and magnetization consists of rearrangement of the molecules in a way that all north poles point in the same direction, as such with the south pole

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46
Q

Magnetic fields originate in _______ and terminate in _________

A

North pole, South pole

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47
Q

What do you call the property when the magnetic flux spreads in the air?

A

Fringing

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48
Q

What is Coulomb’s first law?

A

THe force of attraction or repulsion of two magnetic pole is directly proportional to their strength

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49
Q

What is Coulomb’s second law?

A

The force of attraction between two poles is inversely proportional to the square of the distance between them

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50
Q

Formula of Magnetic attraction

A

F = km1m2/r^2

k=1/4pi(u)
u=uo*ur
ur=relative permittivity
uo=absolute permittivity (constant 33)

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51
Q

The tendency of the magnetic lines of force is to ____________

A

take an easy magnetic path

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52
Q

___(yes/no) lines of force can cross each other

A

no

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53
Q

where is the right hand rule applicable?

A

when determining the magnetic field(conventional current flow)

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54
Q

Formula for Force in a current carrying conductor in a magnetic field

A

F = BILsin(theta)

B=flux density, Wb/m^2 o Tesla
I=current flowing in a conductor, Ampere
L-length of conductor, meters

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55
Q

Formula for Magnitude of flux surrounding a straight conductor

A

phi=14x10^-8IL*log(R/r) Wb

I=current, A
L=length, ft
R=radius of the desired limiting cylinder
r=radius of the conductor

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56
Q

Formula for Magnitude of flux between two parallel conductors

A

phi=28x10^-8IL*log(d-r)/r Wb

d=distance between the conductors

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57
Q

Formula for Force between two parallel conductors

A

F=2I1I2L/d x10^-7

I1,I2 = current in the conductors
L= length of the conductors, Meters
d=distance between the conductors, Meters

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58
Q

Direction of force between two parallel conductors

A

If same current direction, force is Attractive

If different direction, Force is repulsive

59
Q

Formula for Force of attraction between poles of magnets

A

F = km1m2/d^2 Newtons

k=1/4piu0 x10^-7
m1,m2= magnetic pole strength, Wb
d=distance between poles, meters

60
Q

Formula for Magnetic Flux Density

A

B=Φ/A, Wb/m^2

Φ= magnetic flux lines (in Wb)
A= area (in m^2)
61
Q

Reluctance Formula

A

R=L/uA, Ampere-turn/Wb
R=mmf/phi

L=length of the magnetic path, m
A=cross sectional area, m^2
u=permittivity of the material, H/m

62
Q

Formula for Energy stored in a magnetic Circuit

A

1/2R(phi)^2

63
Q

What is Hysteresis?

A

it is the internal friction of molecules, causing the heating of a material

64
Q

What is Magnetomotive force?

A

The force required to establish magnetic field in a magnetic material

65
Q

Magnetomotive force is dependent upon what?

A

Current flowing, A

and number of turns, Turns

66
Q

1 Gilbert is equivalent to_____

A

0.4 (Ampere-Turn)

67
Q

What is magnetizing force or magnetic field intensity?

A

magnetomotive force per unit length required to properly magnetize a given material

68
Q

Formula for Magnetic field intensity formula?

A

H=mmf/L=NI/L ; (At/m)

69
Q

It is the measure of how easily a magnetic field can be created in a material upon application of a magnetic force

A

Permeability (in Henrys per meter)

70
Q

The reciprocal of permeability

A

Reluctivity

71
Q

Hysteresis loss formula is also known as

A

Steinmetz’s Formula

72
Q

What is the formula for Hysteresis Loss

A

Wh=nfBm^1.6

n=hysteresis coefficient
f=frequency, Hz
Bm=Maximum flux density, T

73
Q

Formula for Ohm’s law in magnetism

A

phi=mmf/R ; Wb/Maxwell

74
Q

The property of a magnetic material to allow easily magnetic flux to be established,

A

Permeance

75
Q

Permeance Formula

A

1/R = Wb/At

76
Q

Flux Density and Magnetic Field Intensity of an infinitely long straight conductor

A

B=uI/2pir
H=I/2pir

I - Current in conductor

77
Q

Formulas for Ampere’s Circuital law in magnetism

A

Source of mmf
mmf=NI

mmf drops:
mmf=phi*R
mmf=Hl

78
Q

Total Reluctance in series

A

Rt=R1+R2+R3…

79
Q

Total Reluctance in Parallel

A

1/Rt=1/R1+1/R2…

80
Q

Total FLux in Series

A

Phi(total)=phi(1)=phi(2)=phi(3)

81
Q

Total Flux in Parallel

A

Phi(total)=Phi1 + Phi2

82
Q

Who discovered Charge?

A

Benjamin Franklin

83
Q

Where and when was “electricity” coined?

A

600BC, Greece

84
Q

“electricity” comes from the word _____

A

Amber

85
Q

When you rub Silk on glass, the glass is (+ , - ) charged

A

Positively charged

86
Q

Another term for a positively charged material

A

Vitreous

87
Q

When you rub Fur on Rubber, the Rubber is (+ , - ) charged

A

Negatively Charged

88
Q

Another term for a negatively charged material

A

Resinous

89
Q

A machine used to produce a static charge

A

Van de Graff Generator

90
Q

Coloumb’s Constant(k)

A

K = 1/(4πεo) = 9 x 10^9 Nm^2/C^2

91
Q

Unit of Coloumb’s Constant (k)

A

Nm^2/C^2

92
Q

Unit of Permittivity (ε)

A

C^2/(Nm^2)
or
F/m

93
Q

The Electrostatic force is ____ times greater than the gravitational force of attraction felt by two particles

A

10^36

94
Q

Unit of Electric Field Intensity

A

Volts / m or N / Coloumb

More common as V/m

95
Q

A material that emits equally opposing charges

A

Dipole

96
Q

an electric field emitted by a dipole will have a point, with an E-Field intensity equal to zero, Located at ________

A

Nowhere

no point in an E-Field of a dipole exists an Intensity of zero

97
Q

The Force Vector and the E-Field Vector are always _________

A

Parallel to each other (points at the same direction

98
Q

Gauss Law

A

Flux = ∑(Q / εo)

Q - Charges inside a closed surface

99
Q

What is the E-Field observed when a Charge Q is Distributed uniformly on a spherical surface?

A

The E-Field observed at any point outside the sphere will look like an E-Field emitted by a charge in a single point, as if the charge was only concentrated at the center of that sphere

100
Q

What is the E-Field observed inside a spherical surface with a uniformly distributed charge over its surface?

A

E-Field is 0

Charge(Q) inside is 0 as well

101
Q

What is the E-Field observed in the presence of an infinite sheet of charge

A

Assuming that the sheet is infinitely large, the E-Field Intensity observed AT ANY POINT IN SPACE is:

E = ρs / 2εo

ρs - Surface Charge Density (Coloumb / m^2)
εo - Permittivity of Free Space

102
Q

E-Field BETWEEN equally, but oppositely charged plates

A

E = ρs / εo

ρs - Surface Charge Density (Coloumb / m^2)
εo - Permittivity of Free Space

103
Q

E-Field OUTSIDE equally, but oppositely charged plates

A

E = 0

except at the ends of the plates, where the fringe field exists

104
Q

What does it mean when Coloumb’s force is Conservative?

A

If a particle moves around an E-Field, and will return to its initial position, the summation of work done by the charge to oppose the E-Field as it moves, minus the work done by the E-Field to the particle when the particle moves along with the E-Field, is equal to zero

105
Q

Formula for Work done by a particle from point A to B under the influence of an E-Field

A

W(AB) = ΔPE = Q(test) (VA - VB)

Q(test) - Charge of the moving particle
VA - Voltage @ Point A
VB - Voltage @ Point B

106
Q

Formula for the Speed of a particle from point A to B under the influence of an E-Field

A

Shift solve for ‘v’:
ΔPE = ΔKE
W(AB) = 0.5mv^2

Q(test)x(V(AB)) = 0.5m(v)^2

Q(test) - Charge of the moving particle
V(AB) = (VA - VB)
VA - Voltage @ Point A
VB - Voltage @ Point B

107
Q

The Locus of points around a charge where the Electric Field Intensity and Voltage is equal

A

Equipotential Lines

108
Q

Equipotential lines are (Parallel/Perpendicular) to the Electric Field Lines

A

Perpendicular

109
Q

The Electric Field is obtained by performing a ________ Operator on the __________

A

Gradient Operator on the Voltage
E(vector) = - ∇(Voltage)

Note: Gradient transforms a scalar field into a vector field

110
Q

Formula for Capacitance between two parallel plates

A

C = (εo A) / d
“Seed”

A - Area of plates
d -Distance between plates

111
Q

The electric field inside a conductor is ____

A

E = 0 V/m

112
Q

Charges in a conductor will ______ on the outer surface of a conductor

A

Uniformly Distribute

113
Q

Inside an enclosed surface made out of a conductor, there is no ________ or ________

A

Charge or Electric Field

114
Q

Conductors throughout its material is said to be __________ in terms of voltage

A

Equipotential

115
Q

An enclosed surface build for the purpose of electrostatic shielding

A

Faraday’s Cage

116
Q

What happens when you introduce a charge inside a Faraday’s Cage?

A

Ex. if a positive charge is placed inside, the inner surface of the Faraday’s Cage will be Negatively, but Equally Charged as that of the positive charge inside

but since conductors(The faraday cage) are equipotential (E = 0), the outer surface of the cage will be positively charged, as equally as the negatively charged inner surface

117
Q

What Electric Field Intensity is Required for a High Voltage Breakdown(in air)?

A

3 x 10^6 V/m

118
Q

A Famous example of A high Voltage Breakdown (An electric field of 3x10^6 V/m) is the weather phenomenon called _________

A

Lightning

119
Q

When a High Voltage Breakdown paired with a continuous flow of current occurs, it causes the ________

A

Corona Effect / St. Elmo’s Fire

120
Q

A ______ Magnet is always a permanent magnet

A

Natural

121
Q

An _______ Magnet requires the phenomenon of electromagnetism

A

Artificial

122
Q

When the Relative Permeability of a material (μr) is Greater than or equal to 100, the material is said to be ________

A

Ferromagnetic

123
Q

When the Relative Permeability of a material (μr) is Slightly greater than 1, the material is said to be ________

A

Paramagnetic

124
Q

When the Relative Permeability of a material (μr) is Slightly less than 1, the material is said to be ________

A

Diamagnetic

125
Q

The Most Famous Diamagnetic Material is ________

A

Copper

126
Q

A Diamagnetic Material (Deflects/Attracts) Magnetic Flux Lines

A

Deflects

127
Q

When the Relative Permeability of a material (μr) is equal to 1, the material is said to be ________

A

Non-Magnetic

128
Q

1 Weber is equal to ________ Maxwells

A

1 Wb = 1 x 10^8 Mx

129
Q

The CGS equivalent of Tesla (Wb/m^2)

A

GAUSS:

1 Gauss = 1 Mx/cm^2

130
Q

THEORY: A coil of wire in the presence of a changing magnetic field will “induce” a voltage across the coil

A

FARADAY’S LAW

V = NdΦ/dt

N - number of turns
dΦ - change in Magnetic Flux Lines
dt - as time changes

131
Q

Will a coil of wire in the presence of a static magnetic field induce a voltage?

A

no

based on V = NdΦ/dt, no change in dΦ means no voltage

132
Q

Alternative Magnetic Flux Density Formula

A

B = μH

B - Magnetic Flux Density (Wb/m^2)
μ - Permeability (μ = μrμo) (in Henrys/m)
H - Magnetic Field Intensity (in Henrys or Ampere-turn/meter)

133
Q

Unit for Permeability of Free Space

A

μo - 4π x 10^-7 H/m

Unit is in Henrys / meter (H/m)

134
Q

Formula for alternative interpretation of Faraday’s Law

A

V = L (di/dt)

V - voltage induced in a coil
L - Inductance of Coil (in Henrys)
di - Change in Current
dt - change in time

135
Q

Will there be an induced voltage when the current through a coil is DC?

A

No

based on V = L (di/dt), no change in di means no voltage

136
Q

Combining the two equations for Faraday’s Law gives this equation:

A

V = NdΦ/dt And V = L (di/dt)

NdΦ/dt = L (di/dt)
∫NdΦ/dt = ∫L (di/dt)

Final Equation:

NΦ = Li

N - Number of Turns in a coil
Φ - Magnetic Flux lines
L - Inductance
i - Current

137
Q

Combining:

NΦ = Li, 
B = μH,
H = mmf/ l, 
mmf = Ni  
and B=Φ/A

will give the formula for __________

A 
INDUCTANCE FORMULA: 
B = μH --------EQ 1
B=Φ/A ---------EQ 2
NΦ = Li >>>>>>> Φ = Li/N ----EQ 3
H = mmf/ l --------EQ 4
mmf = Ni --------EQ 5

EQ1 + EQ2
Φ/A = μH&raquo_space;»»»> ADD EQ3 (substitute Φ)
Li/NA = μH&raquo_space;»»» ADD EQ4 (substitute H)
Li/NA = μ mmf/ l&raquo_space;»»> ADD EQ5 (substitute mmf)
Li/NA = μ . Ni/ l

FINAL FORMULA:

L = μ(N²)A / l (in Henrys)
“LUNAL”

μ - Permeability
l - length of inductor coil
N - Number of Turns
A - Area

138
Q

THEORY: a supplement to Faraday’s Law, where it indicates that the polarity the induced EMF in the presence of a changing magnetic field

A

LENZ LAW:

V = -NdΦ/dt

139
Q

The effect observed when electrons are pushed to one side of a conductor that carries current, due to the presence of a magnetic field, Polarizing the conductor, making one side positive, and another negative, that results to a voltage across the width of the conductor

A

Hall Effect

140
Q

Formula for the Hall Voltage in the conductor due to the Hall Effect

A

V(hall) = I*B / [n(qe)d]

I - Current in conductor(Amperes)
B - Magnetic Flux Density (in Tesla)
qe - electron charge (-1.6 x 10^-19 Coloumbs)
d - Thickness of conductor (not Area)
n - Volumetric Electron Density (#e- / m^3)

141
Q

Formula for Electron Density(n) of a material

A

n = ρ(NA) / MM

ρ - Density of Conductor
NA - Avogadro’s Number (6.022 x 10^23 particles/mole)
MM - (Molar Mass (g/mol))

142
Q

Electron Density(n) for copper

A

n(copper) =8.5 x 10^28 (in #e- / m^3)

143
Q

Formula for Drift Velocity ¯_(ツ)_/¯

A

Vd = I / [n(qe)A]

I - Current in conductor(Amperes)
qe - electron charge (-1.6 x 10^-19 Coloumbs)
A - Cross Sectional Area of conductor
n - Volumetric Electron Density (#e- / m^3)

Bryx_Electronics (11 decks)

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